The present invention relates to the manufacture, by coating, of a relatively thin plastic web generally including at least one coating layer, itself comprising a substrate made up of at least one thermoplastic base material, especially a chlorine-containing polymer or copolymer, for example polyvinyl chloride. The coating layer optionally forms the only layer of the plastic web; it may be associated with or bound to any appropriate support, for example a nonwoven of inorganic, for example glass, fibers. Such plastic webs can be employed as floor or wall coverings, as tarpaulins or else as furniture- or motor vehicle coverings.
The present invention will now be introduced, defined, described and discussed with reference to floor or wall coverings obtained in the form of rolls or tiles from a plastic web as described above.
As is known, such coverings include one or more layers obtained by calendering or coating and themselves comprising multiple or varied decorations onto which can be optionally applied a protective layer called a wear layer, the latter contributing mechanical strength and physicochemical resistance to the coverings. These same coverings may also exhibit a relief effect, optionally corresponding to the decoration and obtained mechanically or chemically, for example by inhibition of a foaming of the substrate with one or more coating layers.
In the description which follows and the claims the following expressions carry the meanings given below:
"coating layer" is a layer obtained by applying onto a support a thin layer of material in fluid form, called a plastisol, the plastisol being a dispersion of fine particles of polymer in a liquid mixture of one or more plasticizers; a simple raising of temperature changes the coating layer from the fluid state into the solid state; this is gelling; PA1 "calendered layer" is a layer obtained on an already gelled solid mixture of plastic heated by forced passes between two or more hot rolls. PA1 a) a plastisol is placed or obtained in the pasty state, that is to say in a relatively liquid or semiliquid state, including the plastic substrate in divided form and a plasticizing agent; PA1 b) the plastisol is deposited as a layer onto a flat support to obtain the coating layer in the pasty state; PA1 c) the plastisol is gelled to obtain the coating layer in the solid state, but relatively plastic; PA1 d) optionally, after the gelling state c), the coating layer is grained or goffered. PA1 (a) a plastisol is arranged in the pasty state, including the substrate in divided form and a plasticizing agent; PA1 (b) the plastisol is deposited as a layer onto a flat support to obtain the coating layer in the pasty state; PA1 (c) the plastisol is gelled to obtain said coating layer in the solid state but plastic; and PA1 between the stage (b) of formation of the coating layer and the stage (c) of gelling of the plastisol, at least one stage of powdering is performed, according to which particles of plastic powder are accelerated merely by gravity toward the external surface of the coating layer in the pasty state, and the particles thus accelerated are distributed according to the external surface of said coating layer. PA1 the acceleration is voluntary and the voluntary acceleration and the distribution are performed in such a way that the particles are incorporated homogeneously in at least one, top and/or back, surface layer of the coating layer. PA1 (A) a source of a plastisol in the pasty state including the substrate in divided form and a plasticizing agent; PA1 (B) a station for depositing the plastisol as a layer onto a flat support, to obtain the coating layer in the pasty state; PA1 (C) a station for gelling the plastisol, to obtain said coating layer in the solid state but plastic; PA1 and between the station (B) for depositing the coating layer and the station (C) for gelling the plastisol, a station for powdering is placed. PA1 a source of a plastic powder including particles of at least one thermoplastic material for incorporation; PA1 means for accelerating the particles of the powder toward the external surface of the coating layer in the pasty state and for distributing the particles thus accelerated according to the external surface of said coating layer, which are arranged and controlled in order to homogeneously incorporate the distributed and accelerated particles in at least one surface layer of the coating layer.
In general, to obtain by coating a covering which can be considered similar to at least one plastic web, at least the following stages are linked into a sequence:
It is known in various documents, for example Patent Applications EP-A-0 252 430, GB-A-1 033 923, GB-A-1 569 943, U.S. Pat. No. 3,682,741 and WO-A-87/01972, to incorporate plastic-based particles used to create a decorative effect in the coating layer, for example by encapsulation (EP-A-0 252 430) or else by sedimentation (U.S. Pat. No. 3,682,741).
The process generally used in these documents is a process for the manufacture of a plastic web including at least one coating layer comprising a substrate made up of at least one thermoplastic base material, especially a chlorine-containing polymer or copolymer, for example polyvinyl chloride, said process including at least the following stages:
The process described above consequently requires the use of a plastisol in the pasty state, made up traditionally of the thermoplastic base material, for example polyvinyl chloride, in divided or discrete form, dispersed in a plasticizing agent in liquid form.
However, the use of plastisols of this type does not remain problem-free, because it requires the use of a large quantity of plasticizers, for example a proportion of plasticizer of between 55 to 65 per cent by weight of the quantity of base plastic, to obtain a viscosity which is acceptable for the coating tools, such as doctor blades and to allow good deaeration of the coating layer(s) formed. The plasticizers most commonly employed are organic derivatives of acids such as phthalic acid, phosphoric acid, benzoic acid, adipic acid, citric acid, glutaric acid, lauric acid, sebacic acid, azelaic acid, capric acid and trimellitic acid. On the other hand, this large quantity of plasticizers does not make it possible to obtain a coating exhibiting acceptable surface properties once the layers are gelled, and the coating exhibits in particular a stain resistance and soiling by pedestrian traffic which rule it out, a greasy and adhesive feel, an unpleasant odor, excessive flexibility and an exaggerated and permanent tendency to exudation.
In order to overcome these disadvantages the manufacturers of coverings often add plastifiers to replace a proportion of the plasticizers, and this also makes it possible to obtain viscosities which are lower than with plasticizers alone, the low viscosities being desired to allow coating at high speed and therefore economically advantageous. These are generally low-viscosity organic liquids, for example petroleum cuts with a boiling range of between 130.degree. C. and 320.degree. C., or products such as dodecylbenzene and texanol isobutyrate. The coating layer formulations, for example PVC-based, may contain plastifiers in a proportion of 5 to 20 per cent by weight of the quantity of base plastic, and this allows the proportion of plasticizer in the formulation to be lowered to approximately 40 to 50 per cent by weight of the quantity of base plastic. The feel and the stain resistance thus become acceptable.
Despite this advantage, the use of plastifiers creates another problem, namely in that they give rise to large volumes of volatile organic components (VOC). In particular, the use of plastifiers does not make it possible to meet the new requirements relating to air quality. Volatilization of these components on industrial sites, for example during the gelling of the plastic layers, is unavoidable and requires costly plant for the condensation and trapping of the effluents. Furthermore, even after gelling, the coating comprising plastifiers continues to give off VOCs by evaporation throughout its use, and this is reflected in odor problems and headaches in places where these products are installed. New European legislations will set a maximum quantity for the release of these VOCs and the plastifiers currently employed are aimed at in particular.
It is also important to stress that the use of plastifiers does not make it possible to reduce the quantity of plasticizers below a certain proportion.
To avoid employing plastifiers, and in coating technology, it might be assumed that it would be sufficient quite simply to increase the quantity of plasticizer in the base plastisol, as overplasticizer, in order to keep a viscosity which is compatible with processability on production equipment. This solution unfortunately gives a final product in the form of a web which is adhesive and unsuitable in particular for use as floor covering.